Homemade Crockpot Yogurt

I've made crockpot yogurt a few times following this tutorial on A Year of Slow Cooking. Both times it was sour... really sour. I ate it okay in oatmeal and with granola and fruit but even with adding honey or sugar my kiddos wouldn't go for it. It seemed like it should have tasted better so I tried again and I found this little post . Wah-la! It turned out delicious.

HERE's what I used:
1/2 gallon whole milk
slow-cooker (mine is 3-quarts I think)
1/2 cup plain yogurt with cultures (I used Mountain High)
cooking thermometer (I used a meat thermometer)
TO make it GREEK:
coffee filters
colander
large bowl
space in the fridge for bowl and colander

HERE's What I did:
Put 1/2 gallon of whole milk in slow cooker on a day when I'd be mostly home so I could babysit it a bit. (I believe in fat, so I've never tried lower fat milk). Turn on low for 2 1/2 hours. I checked the temperature and found that it wasn't to 180 degrees so I turned it on high and checked it 30-40 minutes later (hoping it wouldn't burn). It didn't burn and it came up to 180 degrees. (If you don't get it to 180, it doesn't kill any extra bacteria your milk might have and I think that's why mine was so sour. The low setting only got it to about 140 in 2 1/2 hours).
I unpluged my cooker. Then I let it sit for about 3 hours and checked the temperature again, it was down around 115 (the other post said you want it to be 115-120). I dished up 1/2 cup plain yogurt in a container where I could add more volume and added about a 1/2 cup of the warm milk (being grateful the whole time I'm not pregnant because that warm milk smell... ugh!). I mixed those together and then stirred them back into the crock. I covered it in some towels and let it sit 6 -7 hours. To thicken it to "Greek" yogurt I lined a colander with coffee filters (purchased at the dollar store) and put it over a big bowl then I stuck it in the refrigerator overnight. All the whey drains out and you are left with deliciously thick, creamy yogurt. This time it wasn't sour! Hooray. If you want it to be thinner I imagine you could just stir some of the whey back in. Save the whey and replace it for liquid in bread recipes. I've done this and it makes really tender bread, though it seems to dry out even faster than my regular bread.
Yeild- about 32 oz. greek yogurt or 64 oz. regular plain yogurt

So here's a condensed recap without all my comments:
1/2 gallon milk
1/2 cup yogurt

Warm milk until 180 degrees.
Turn off crockpot.
Let cool until 115-120 degrees.
Stir in 1/2 cup plain yogurt with cultures.
Cover in thick towel to keep warm.
Let sit 6-8 hours.
Take out and either put in containers to store in fridge or put in lined colander to drain whey and put in fridge.